Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, allowing them to utilize the allocated radio spectrum without interfering with each other. Multiple access systems coordinate access between multiple users. The users may also share access via different methods such time division multiple access (TDMA), code division multiple access (CDMA), or spatial division multiple access (SDMA). These protocols are utilized differently, at different levels of the theoretical OSI model.
Frequency bands are allocated either in distributed manner or in localized manner in frequency domain. In other words, frequency resource allocation is largely classified into localized resource allocation and distributed resource allocation.
Localized resource allocation generally refers to a method for allocating a plurality of subcarriers which are contiguous in physical domain to a single user. Scheduling gain, such as multi-user diversity gain, can be achieved by localized resource allocation.
In contrast, distributed resource allocation refers to a method for allocating a plurality of subcarriers which are not contiguous in physical domain to a single user. Frequency diversity may be achieved by distributed resource allocation.
Resource allocation can be performed in units of a resource unit (RU) or a set of RUs. A RU consists of M subcarriers in frequency domain, and of N orthogonal frequency division multiple access (OFDMA) symbols in time domain. For example, a RU may consist of 18 (M=18) subcarriers by 6 (N=6) OFDMA symbols. The plurality of subcarriers constituting a RU may or may not be contiguous in physical frequency domain. The plurality of OFDMA symbols constituting a RU is contiguous in physical time domain.
A RU is classified into one of localized RU and distributed RU (DRU). A localized RU is composed of a plurality of subcarriers which are contiguous in physical frequency domain, and can be used for the localized resource allocation. A distributed RU is composed of a plurality of subcarriers which are not contiguous in physical frequency domain, and can be used for the distributed resource allocation. The term “localized RU” may also called as “contiguous RU (CRU)”.
Above mentioned RUs are used for IEEE Standard 802.16. IEEE Standard 802.16 is a product of IEEE 802.16 Working Group on Broadband Wireless Access Standards, which was established by IEEE Standards Board in 1999, to develop standards for the global deployment of broadband Wireless Metropolitan Area Networks. The Workgroup is a unit of the IEEE 802 LAN/MAN Standards Committee.
Although the 802.16 family of standards is officially called WirelessMAN in IEEE, it has been commercialized under the name “WiMAX” (from “Worldwide Interoperability for Microwave Access”) by the industry alliance called the WiMAX Forum. The mission of the Forum is to promote and certify compatibility and interoperability of broadband wireless products based on the IEEE 802.16 standards.
The most popular IEEE 802.16 standard is IEEE Std 802.16e-2005 Amendment (hereinafter 16e) that is widely being deployed around the world in more than 100 countries by more than 300 operators. 16e was completed in 2005 and the WiMAX Forum certified products were released starting 2007.
According to 16e, a localized RU and a distributed RU is distinguished by time zone in a frame defined by 16e. That is, a localized RU and a distributed RU are multiplexed in time division multiplexing (TDM) manner as shown in FIG. 1. FIG. 1 shows an exemplary frame structure use in IEEE Standard 802.16e.
If a localized RU and a distributed RU are multiplexed in TDM manner as in 16e, the flexibility of the ratio of the number of users using localized RUs to the number of users using distributed RUs generally decreases. Therefore, in a view of the flexibility of the localized RU users and the distributed RU users mixing ratio, it is beneficial to multiplexing a localized RU and a distributed RU in a sub-frame in time division multiplexing (TDM) manner, which is adapted in 3rd generation project partnership long term evolution (3GPP LTE) as known in the wireless communication industry. Herein, the sub-frame is a set of time contiguous OFDMA symbols which constitutes a radio frame.
Generally, in order to design a FDM multiplexing scheme for multiplexing localized RUs and distributed RUs, it can be considered followings; first, scheduling gain of localized RU users; second, frequency diversity gain of distributed RU users; third, signaling overhead, and last, scheduling diversity.
In particular, for the case that logical frequency bands are divided into several logical frequency zones (LFZ) as in fractional frequency reuse (FFR) scheme, it is necessary to develop an effective FDM scheme for localized and distributed RUs. The term “logical frequency zone” may be also called as “frequency partition” hereinafter.